1. Field of the Invention
The present invention relates to a silent chain suitably used as a timing chain that transmits rotations of a crankshaft to a camshaft in an engine, and more specifically to a silent chain and a silent chain transmission configured such that a back face of the silent chain is in contact with and is guided by a chain guide.
2. Description of Related Art
In general, a silent chain is composed of inner link plates each having a pair of teeth that engage with teeth of a sprocket, guide link plates disposed on both sides of the inner link plates and guide the silent chain such that the silent chain does not deviate from the sprocket, and pins fixed to the guide link plates and flexibly connecting the inner link plates. When the silent chain is used as a timing chain in particular, a back face of the silent chain is in slidable contact with a chain guide such that the silent chain is guided while receiving a predetermined tension and while preventing vibrations thereof.
Conventionally, there is known a silent chain configured such that lengths from a line connecting centers of pin holes to back faces of an inner link plate and of a guide link plate are equalized. It is also proposed to use a low rigid guide link plate having a crotch portion as a guide link plate and, in consideration of a clearance between a pin and a pin hole of an inner link plate, to set a length from a line connecting centers of the pin holes to a back face of an inner link plate such that a value of the length is equal to or greater than a value to which ½ of the clearance is added to a length from the line connecting the centers of the pin holes to a back face of a guide link plate to which the pin is tightly fitted as disclosed in Japanese Patent No. 4618846.
Each inner link plate of Japanese Patent No. 4618846 has the back face which is a straight flat face. It is noted that the back face is a part of the inner link plate between lines orthogonal to the straight line connecting centers of the both pin holes and passing through the centers of the pin holes. This arrangement makes it possible to guide the whole back face of each inner link plate in contact with the chain guide, to prevent back faces (ear portions) of the guide link plate having the crotch portion from strongly abutting against with small contact faces, and to prevent edge-like abrasion mark from being made on a guide face end portion of the chain guide.
However, the silent chain described above increases a friction loss because the whole back face of the inner link plate of the silent chain is in slidable contact with the chain guide. Still further, some guide link plates cause a gap between the back face thereof and the guide face of the chain guide, destabilizing behaviors of the chain, e.g., causing vibrations in width and twisting directions. Such destabilized behaviors of the chain may cause improper engagement of the inner link plates with a sprocket, generate engagement noise and drop transmission efficiency of the chain.